Gartner anticipates touch screens (in Smartphones and midrange phones) to grow nearly 97% approaching 363 million units worldwide in 2010. By 2013 touch screens are expected to account for 58% of all mobile devices sold worldwide and more than 80% in the North American and Western European markets. Other market analysts anticipate that by 2015 there could be as many as 5 billion Smartphones in operation. In addition, the new tablet computers (such as the Apple iPad and Samsung Galaxy Tab) are gaining rapid acceptance with consumers. Apple is expected to sell 30 to 40 million iPads in 2011 and the Samsung Galaxy Tab has sold more than 1 million units since its release in November of 2010.
Resistive and capacitive touch screen technologies require materials that are both transparent and conducting to be functional. Indium Tin Oxide (ITO) is currently the most widely used metal oxide for touch screen sensor applications as it is optically transparent and is a fair conductor. ITO is commonly employed to make transparent conductive coatings for liquid crystal displays, flat panel displays, touch panels, solar panels and aircraft windshields. In resistive touch screens, when a user touches the screen with a finger or a stylus, the ITO film is pushed into contact with the ITO glass producing a voltage signal allowing a processor to compute the coordinates (X and Y) of the touch event and process the appropriate response to the touch point.
Although ITO is a mature and widely-used technology, it is not ideal. The main issues with ITO are the limited supply and the rising cost of indium. The supply issue is exacerbated by the fact that indium is a rare earth metal and is nearly exclusively controlled by the government of China. Other drawbacks associated with ITO have to do with the vapor deposition manufacturing process, which is expensive and cumbersome. The material itself is fragile and lacks flexibility and, compared to copper, indium is a relatively poor conductor. As a result, for more than a decade researchers have spent millions of dollars seeking a better and more cost-effective alternative. Some of these research efforts to find a transparent conductor have included the use of materials such as carbon nano-tube conductive coatings, thin metal films, conductive polymers (ICPs), and aluminum zinc oxide (AZO). To date, all of these materials have demonstrated significant disadvantages to ITO and are not currently commercially viable options.
In addition to the limitation of the ITO element, electrode patterns in touch sensors can only be printed at certain dimensions or resolution, specifically only electrode pattern structures above 25 microns are supported by current printing technologies.